Is there a way to use monad comprehensions with Kotlin Flow

Question

Kotlin coroutines and Arrow are a nice way to avoid nesting flatmaps, introducing monadic comprehensions in Kotlin. However Kotlin's Flow type still relies on declarative flatmapping, so we get into a mixture of direct and declarative styles:

    override suspend fun findAll(page: Pageable): Either<BusinessException, Flow<PageElement<ClientOut>>> = either {
        val count = clientRepository.count().awaitSingle().bind()
        return clientRepository.findByIdNotNull(page).asFlow()
            .flatMapMerge { client ->
                flow { emit(mapDetailedClientOut(client)) }
            }
    }

val count has been bound inside the either {...} comprehension. However, there doesn't seem to be a way to do the same with Flow, forcing us to nest a flatmapMerge().

Is there a way to do it, or is it planned to be somehow included in the near future?

Answer 1

Sadly there is currently no way to build comphrehensions for the KotlinX Flow datatype, since Coroutines in Kotlin only support for single-shot emission/bind.

Therefore it's only possible to build comphrensions for data types with 0..1 elements such as Either or Nullable, but not 0..N like the Flow or List data types.